I would argue that fent became an issue only after the oxycontin et al. peddling was slowly curtailed; together with fent precursors becoming absurdly cheap to procure and process, compared to other opiates. Users originally hooked on the pills needed a replacement, and as suddenly the chemistry got much cheaper, everyone switched to fent. The physical volume of illicit substance you need to smuggle is also lower with fentanyl, so I'm sure that would have played into this trend as well.

If you want to find where to point the finger to, the systems that let prescription opiates be prescribed with such reckless abandon is a good superficial target. Getting political here - if you want to find the very root cause of all this, I would present the institutions that prevent the implementation or otherwise erode preexisting social safety-nets as the culpable party.